Method of separating differentially heated particles



United States Patent "ice m 1 Patented July 9, 1963 1 Frank R. Ofner, Portland, Greg, assignor to Industrial 1 l 2 P ject of the invention is that of providing a process and ap- 3,997,159 paratus for washing wheat, other grains and the like, PROCESS FOR CLEANING GRANULAR which will optimize in a single washing stage the advan- MATEREALS tages now gained in multiple washing stages, and wherein Powertronix, Inc., Portland, Greg, a corporation of the lsylstem compact with the result that it gregon occupies an ins gnificant amount of space compared to Ffled May 26 1953SBLN0737366 the space reqmrement of prior systems (for example, 3 Claims. (ill. 209-2) a space of about 5 x 12' as opposed to several floors of equipment for washers having a capacity of about 330 This invention relates to a process and apparatus for bushels per hour). cleaning granular materials, and more particularly to such Still another object is that of providing a system of the a process and apparatus for washing grains such as wheat. character described, wherein the apparatus because of Many granular materials much be cleaned as a step its structural simplicity and the minimization of relatively in the processing thereof, and this is especially true of moving components, requires but a small initial investgrain. For example, it was early discovered that a num- 15 ment, has a low maintenance cost and has a low power ber of advantages accrued from washing wheat prior to demand. Moreover, the installation expenses are low and converting the same into flour. Among such advantages the equipment can be installed quite rapidly and, if deare the removal of smut and dirt, loosening of the outer sire an integral y beeswing, an improvement in the general sanitary condi- Yet another object is in the provision of an improved tion of the grain, and the production of a more uniform Washing process for wheat and the like and for apparatus flour having :a low ash content, improved color, better to carry forth the same, that materially decreases the milling qualities and an increase in the patent flour prodamage to the grain that is inherent in the scouring action duced. In view of these advantages, it is quite common provided by present washers, but which at the same time today for millers to wash wheat before grinding the same affords a much better and more thorough cleaning of the into flour. grain whereby the product yield is greater. A further Essentially, a single type of washer is in use, and it comobject is to provide 8. Wash g n y g System may ri a large horizontally di d cylinder, Wh t and be noted that the term washer as used in the trade comwater are fed to a closed section of the cylinder where Pfehends y g Stage, Consequently the concepts the washing action takes place. A revolving spiral ribbon of washing and drying per se are not necessarily distinwithin the cylinder carries the wheat after washing through g the ehehaetef desefihed, wherein a much a perforated section thereof, wherein the wheat is rinsed. r Control Of the moisture Content of the end P is The rinsing action is accomplished and controlled through attained-so much better in fact that the control may be manual or mechanically operated valves that determine o s dercd substantially absolute. the quantity of water delivered to the cylinder. There- Yet further Object is in the Provision of Y in after, the spiral ribbon continues to advance the rinsed which the wash water is used to its capacity whereby a grain to a further section of the cylinder wherein a constant much more thorou Washing 0f the g ar ma erial i flew of ir, actuated by the movement of the ribbon, reattained per unit of wash water, with the result that the moves portions of the surface moisture and, in conjuneover-all consumption of wash water is diminished. Addition with the centrifugal force developed which drives ofi tional objects and advantages of the invention will become additional water, partially drys the grain. In addition, a apparent as the specification develops. constant air flow is circulated through the grain and con- An embodiment of the invention is illustrated diagramtinues the drying action until the wheat is discharged. metieelly in the Single View which comprises the drawing Although it is common to wash grain and oftentimes hereof. essential because of the sanitation controls imposed by the The process and apparatus illustrated in the drawing Federal Food and Drug Administration, a number of discomprise three stages that, for identification, may be desigadvantages are attendant with the washing process. Such nated as mixing, washing, and separating and drying. The disadvantages include an excessive increase in the moisture drawing is Provided With legends p ing to t content f the grain; the difiiculty of obtaining an adequate nomenclature and indicating the structural components water supply, which must comprehend three to five gallons omprising parts thereof. of water per bushel of grain; the additional power cost of The first stage comprises a mixer 10- of inverted, frustooperating the washer :appara us; and th dditi l majnconical configuration having a conduit 11 feeding into the tenance requirement cannot be overlooked as an economic hollow interior adjacent the upper end thereof, and which factor. Other disadvantages which have existed heretois adapted to supply liquid or wash water thereto. Also fore but which have been overcome in the manner discommunicating with the interior of the mixer 10' is a conclosed in my patents, Nos. 2,835,984 and 2,835,985, are duit 12 through which granular material such as wheat or th l f grain n-i d fi b the wa h water, the di other grain is fed thereto. The conduit 12 may comprise posal of the wastes, and the high water costs resulting a portion of a screw conveyor, and if so will have a feed from the inability to reuse the wash water. screw 13 cooperatively arranged therewith. It will be Other negative aspects of the general cleaning process noted that both of the conduits 11 and 12 have elongated (water washing being one step thereof) are evidenced openings that communicate with the mix'er 10 along an in the high initial cost of the equipment employed and the arc of the surface thereof whereby the infeed of the ma- Vast amount of space required, which may encompas terials, and particularly the wash water, results in a swirlseveral floors in a mill and incorporate as many as sevening motion thereof wherein the material tends to move teen separate cleaning steps. Additionally, the w he through convolutions following the surface contour of are difficult to operate and, as a consequence, are often the mixer. This results in a thorough and intimate mixing improperly used so that the grain is not adequately cleaned, of the liquid and solids. d even wopse acquires la, gummy coating thereon. The lower end of the mixer 10 is provided with an out- In view of the desirability and frequent necessity of let communicating with a pipe or conduit 14 that diswashing grain, an object of the present invention is to charges into the casing 15 of a pump denoted in general provide a process and apparatus for accomplishing the with the numeral 16. The pump is preferably of a large same which will overcome a number of the important disadvantages inherent in the prior art systems. Another obvolume, low head type; and in the form shown, has multiple stages indicated with the numerals 17, 18;, and 19,

s MM

July 9, 1963 3,097,160

' s. R. RICH METHOD OF SEPARATING DIFFERENTIALLY HEATED PARTICLES Filed Nov. 50, 1959 5 Sheets-Sheet 2 I I) I /9 FIG.6

INVENTOR.

STANLEY R. RICH Wag $1M ATTORNEY July 9, 1963 s. R. RICH 3,097,150

METHOD OF SEPARATING DIFFERENTIAL-LY HEATED PARTICLES Filed Nov. 30. 1959 s Sheets-Sheet a 5 5 5 /5 Q Q Q F l G. IO

INVENTOR.

STANLEY R. RICH ATTORNEY July 9,1963 s. R. RICH.) 3,097,160

METHOD OF SEPARATING DIFFERENTIALLY HEATED PARTICLES Filed Nov. 50. 1959 5 Sheets-Sheet 4 l2- 6 6/ (g WW6 IN UT (RAW PPARTICLE F AIR UNDER REGULATED F G. PRESSURE INVENTOR.

STANLEY R. RICH ATTORNEY July 9; 1963 s. R. RICH ,160

METHOD OF SEPARATING DIFFERENTIALLYV HEATED PARTICLES Filed Nov. :50. 1959 5 Sheets-Sheet 5 7 ,4 GENERATOR g: TERMINATION L C fi L\ \I I W r 95 |7I F I G. IS F I G. I7

'I'IIIIJIIIIIIIIIIA HIGH PRESSURE 7 /Q4 AIR I g INVENTOR. i

STANLEY R. RICH ATTORNEY Patented July 9, 1963 3,097,160 METHOD OF SEPARATING DIFFERENIIALIJY HEATED PARTICLES Stanley R. Rich, West Hartford, Conn., assignor of twenty percent to Alfred H. Rosen, Newton, Mass, ten percent to William W. Sellew, Port Chester, N.Y., and ten percent to Robert E. Cohn, Bloomfield, Conn.

Filed Nov. 30, 1959, Ser. No. 856,232 6 Claims. (Cl. 209-4) This invention relates in general to the separation of particles of a given material from a mixture of particles of two or more materials, and more specifically to new methods and means for processing a mixture of particles in the dry state, without the use of water or any other liquid, to achieve such separation.

The primary object of this invention is to provide new and improved methods and means for separating individual specific types of particles from a mixture of various types of particles. It is a further object of the invention to separate metallic particles, including nonmagnetic particlcs, from nonmetallic particles in a mixture. It is another object of the invention to separate important, or valuable minerals from less important and less valuable minerals in such mixtures as are found in mining areas. Another object of the invention is more efficiently to separate individual components of a particle mixture so as to be able to recover even extremely minute or trace amounts of valuable minerals from collections of spent quantities of original mixtures which have passed through conventional and less efficient methods of separation. Such spent mixtures are sometimes referred to as railings.

It is another object of the present invention to process such particle mixtures in the dry state, without recourse to water or other liquids, or to flotation methods, or to other techniques commonly used, for example, in the recovery of valuable minerals from native ore. It is still another object of the present invention to recover particles from such mixtures which are smaller than have ever been economically recovered by earlier and more conventional techniques. For example, it is an object of the invention to be able to recover certain types of metallic particles in the particle size range of 0.1 to 100 microns in diameter, a range of particle sizes previously considered unrecoverable by conventional methods. It is a specific characteristic and object of the present invention that gold particles may be separated from sand or tailings without requiring the use of liquids. It is still another important object of the present invention to provide such new methods and means in which relatively minute amounts of power are required in order to effect such separations. A further object of the present invention is to provide such methods and means which are useful to separate all forms of particles, whether metallic or nonmetallic, and all kinds of metals, whether magnetic or nonmagnetic, from a mixture of particles, and which are particularly useful to recover precious metals such as gold, platinum and rhodium from particle mixtures such as sand and ore tailings in which they are contained.

According to the invention, a mixture of particles of two or more different types or materials is treated to separate particles of a first of said types or materials from the mixture by selectively heating particles of the first type or material to a temperature greater than the remainder of the mixture, and selectively capturing heated particles of the first type or material with a temperaturesensitive body in contact therewith. The invention makes use, for example, of radio-frequency induction fields, timevarying electrostatic fields, electromagnetic wave fields, and other forms of energy in order selectively to raise to ferences in their relative temperatures.

a desired temperature only those components of a mixture which it is desired to separate from the mixture. The invention further contemplates the use of temperaturesensitive material such as paraffin wax, thermoplastic materials, and other materials which can be softened by a Warm or hot particle and thereby become adherent to, or capture, such particles selectively as compared with particles at lower temperatures. It is a further object of the invention to provide methods and means to selectively capture particles in a mixture in accordance with dif- A still further object of the invention is to provide methods and means for achieving such capture on a continuous basis.

The foregoing and additional objects and novel features of the invention will become apparent from the following description of certain embodiments thereof. This description refers to the accompanying drawings, where- FIG. 1 is a side-sectional view of magnetic field particle separating apparatus according to the invention;

FIG. 2 is a section along line 22 in FIG. 1;

FIG. 3 is a side-sectional view of a modification of FIG. 1;

FIG. 4 is a section along line 44 in FIG. 3;

FIG. 5 illustrates circuits useful to produce magnetic fields for the apparatus of FIGS. 1 and 3;

FIG. 6 is a magnified sectional view of a particle collecting medium and collected particles;

FIG. 7 is a top view of apparatus like that of FIG. 1 modified to include stirring devices;

FIG. 8 illustrates schematically the use in series of a plurality of apparatus arrangements according to FIG. 1;

FIG. 9 is a partial top view of FIG. 8;

FIG. 10 illustrates schematically the use in series of a plurality of apparatus arrangements according to FIG. 3;

FIG. 11 is a side-sectional view of an electrostatic field producing arrangement;

FIG. 12 is a section along line 1212 of FIG. 11;

FIG. 13 illustrates a circuit useful to produce electrostatic fields with devices according to FIGS. 11 and 12;

FIG. 14 is a side-sectional view of particle fluidization apparatus employed with the invention;

FIG. 15 is a side-sectional view of particle accelerating apparatus employed with the invention;

FIG. 16 is a diagrammatic side view of an electromagnetic field producing arrangement;

FIG. 17 is a section along 1717 of FIG. 16;

FIG. 18 is a modification of FIG. 16; and

FIG. 19 is a section along line 19-19 of FIG. 18;

Referring now to FIGS. 1 and Q, a magnetic field coil It) is supported on inner coil form 11 and covered by an outer coil form 12., respectively, both made of electrically nonconductive material. These elements are hereinafter sometimes referred to as a magnetic field unit. The coil 10 may be made of wire or hollow tubing, for example, copper tubing, depending upon the frequency of operation for which the coil is intended. The inner coil form 11 and the outer coil cover 12 may be square in cross section, as shown in FIG. 2, or if desired, they may be round or take any other convenient form. A platform 13- made of electrically nonconductive material is disposed across the approximate center of the inner coil form 11, being, if desired, mounted in that form by means of cement or screws (not shown). A web or elongated sheet of particle receiving material 14, to be described in greater detail below, is carried through the coil 10 on the platform 13, in the direction of the arrow 15. A supply roll 16 of the particle receiving material 14 is disposed at one end- (the left hand end in FIG. 1) of the magnetic field unit and a take-up roll 17 is disposed at the other end to receive the web 14 as it comes through the magnetic field unit. The supply and take-up rolls rotate in the direction ated by the coil 19 when the latter is operated for induction heating of the metal particles 19.2, as will be described in greater detail below. The electrically conduc tive particles 19.2 become heated by this magnetic field, by the process of induction heating, and adhere to the web 14, being thereby captured by the web as will be described in detail in connection with FIG. 6. The electrically nonconductive particles 19.1 do not simultaneously become heated. As the web 14 progresses toward the right in FIG. 1 (arrow 15), and is taken up on the takeup roll 17, the surface of the web becomes vertical and the electrically nonconductive particles 19.1 fall off the web. The electrically conductive particles 19.2 which have adhered to the web remain captured by the web as .the web is rolled onto the roll 17 (as is shown in FIG. 1),

and are thereby separated from the particle mixture 19 and collected. The combination of a hopper with feed 18 and a selective heating unit 11l11-12 is sometimes hereinafter referred to as selective particle separating set A.

' FIGS. 3 and 4 illustrate another manner of employing a magnetic field to separate electrically conductive and nonconductive particles from a mixture of the two. As is shown in FIG. 3, a coil 20 is supported on a coil form 21 and covered by an outer cover 22. The elements 20, 21 and 22 are a magnetic field unit which is functionally similar to the elements 10, 11 and 12, in FIG. 1. A hopper feed 23, similar to the hopper feed 18 in FIG. 1, drops the mixture of particles 19 through the magnetic field unit 20212 2, where the mixture is acted upon by the magnetic field created by the coil 20, prior to coming into contact With the web '14. That is, the mixture 19 is acted upon by the magnetic field on the way to the web 14, which is advanced continuously under the hopper feed 23 in the direction of the arrow 15, while resting upon a platform 24 which is similar to the platform 13 in FIG. 1. Take-up rolls similar to the rolls 16 and 17 in FIG. 1 may be present in the arrangement according to FIGS. 3 and 4, but are not shown in these figures to simplify the illustration of differences between the embodiment of FIGS. 1 and 2 and this embodiment. The heated particles of electrically conductive material will again adhere to the web 14 and be captured by it, while the particles of electrically nonconductive material, being for all practical purposes unheated, will not adhere to it. Separation of adhering and nonadhering particles may be accomplished as in FIG. 1. The combination of a hopper with feed 23 and a selective heating unit 202122 is sometimes hereinafter referred to as selective particle separating set B.

FIG. illustrates circuits for providing electric energy for driving magnetic field coils, such as the coil in FIG. 1 or the coil 29 in FIG. 3, for induction heating of metal particles. A coil 31) is indicated schematically as wound on a coil form 31 and driven by an electronic oscillator, for example, a Hartley oscillator 32 comprised of the usual components and coupled to the coil by means of a transformer 33. A radio frequency choke 34 (useful for the purpose to be described immediately below) is provided in the connection between the transformer 33 and the coil 30. The Hartley oscillator 32 includes a vacuum tube 32.1 and terminals 32.2 and 32.3 (labeled B-+ and B respectively) for the operating high voltage.

An operating frequency in the range of 4QQ kc./sec is suitable for inductively heating particles of electrically conductive material which are above approximately microns in cross-sectional size. On the other hand, for induction heating of particles of electrically conductive material which are below approximately 100 microns in size, it is preferable to use a frequency in the range of about 40 megacycles per second. If desired, the coil 30 can be driven at a frequency in one of these ranges, and a second coil 40 can be provided and driven at a frequency in the other of these ranges. FIG. 5 illustrates such an arrangement, in which the above-described Hartley oscillator circuit 32 and coil 31} are arranged for operation at about 400 kc./sec., and a second Hartley oscillator circuit 42 and the second coil 49, interwound with the firstnamed coil 30, are provided and arranged for operation at approximately 40 megacycles per second. The second oscillator circuit 42 includes an electron tube 32.1 and B]- and B terminals 4-2.2 and 42.3, respectively. This oscillator circuit is connected to its coil 41? via blocking condensers 43.1 and 4-3.2. These blocking condensers serve the function of preventing 400 kc./sec. signals from the first coil 30 from entering the second oscillator circuit 42. In the same manner, the RF choke 34, which is connected in series between the transformer 33 and the first coil 39, prevents the 40 megacycle per second signal from the second oscillator circuit 42 from entering the first oscillator circuit 32. Each of the -B+ terminals is connected to the anode of the respective electron tube via a radio frequency choke 35, 35, respectively.

It will be appreciated that the apparatus of FIG. 1 or FIG. 3 may be operated in the range of either of the frequencies 400 kc./sec. or 40 megacycles per second or some other frequency range, and that if desired two sets of coils may be wound on the coil form 11 or 21 and two frequency ranges may be used.

It will be appreciated also that particles of an identical or similar metal can be separated on the basis of their relative sizes by choosing an operating frequency suitable for heating particles in a desired size range to a higher temperature than particles of other sizes. Thus, as will be apparent from explanatory computations set forth below, gold particles of sizes 25 to 75 microns in diameter can be selectively separated not only from sand, but also from other metals of larger sizes, by using a frequency in the range from 10 to 50 megacycles per second.

Referring now to FIG. 6, which shows an enlarged partial cross-sectional view of the web 14, the web is made of a base strip 51, which may be paper, on which there is coated or otherwise adhered a surface coat 52 of material which can be melted by hot particles 53'. When the heated electrically conductive particles on the web 14, whether heated prior to arriving at the web (FIG. 3) or after arriving at the web (FIG. 1) come in contact with the surface coat 52, they melt the coat and penetrate varying distances into it. The coat then flows over the particles for a short time until it again freeze and partially covers the particles as is shown in FIG. 6. The web 14 may be conveniently made of waxed paper in which case the base 5-1 is paper and the coat 52 is wax (e.g., paraffin wax). The particles 53 shown in FIG. 6 are the same as the particles 19.2 shown in FIG. 1. In this manner, electrically conductive particles selectively heated in a mixture of electrically conductive and electrically nonconductive particles can be continuously captured on a web 14 which then may be rolled on a take-up roller 17 (FIG. 1), if desired, for convenience in storing and shipping.

The action of the web 14 by which it captures heated particles 53 requires only that the particles be hot enough to melt or soften the particle receiving material 53 at the time when the two are in contact with each other. Since paraffin melts at about 55 eentigrade (Handbook of Chemistry and Physics, Chemical Rubber Publishing Company, 29th edition), this requires a relatively modest temperature rise, as compared with the usual uses to which inductive heating apparatus is put. There is no need to melt or fuse the metal par-ticles to each other. Thus, unlike the usual processes employing inductive heating, the process of the present invention is operable with the particles which are to be heated separated from each other so that they are individually heated; there is no need to pass a current from one particle to the next, and in this respect the use of induction heating according to the present invention to heat individual metal particles of sizes in ranges of the order of microns, for example, is unlike any use for induction heating apparatus heretofore known to the art.

In order to improve the distribution of particles from the mixture 19 on the surface of the web 14, it is desirable in some cases to employ stirring means. FIG. 7 illustrates one method of stirring these particles, in which nozzles '55 are disposed above the web 14. FIG. 7 is a top view of an apparatus according to FIG. 1 and like par-ts have the same reference characters in these figures. The nozzles 55 are located in close proximity to the top surface of the web 14, as is schematically illustrated by one nozzle 55 in FIG. 1. It will be appreciated that the nozzles 55 are in practice connected to a source (not shown) of pressurized air or other gas which upon being fed at a proper velocity toward the surface of the web 14 will stir the particles of the mixture 19 which are present on the surface. Similar stirring means can be employed in apparatus according to FIG. 3. Likewise, other forms of stirring mechanism, such as mechanical or electromechanical vibrators, may be employed, in place of gaseous-stirring, if desired. Such vibrators could, for example, be attached to the platform 13 (FIG. 1) or 24 (FIG. 3).

FIGS. 8 and 9 illustrate 'a plurality of selective particle separating sets A1 and A2 according to FIG. 1 employed in series with a single particle collecting web 14 to increase the concentration of electrically conductive particles captured on a given web. In FIG. 8 the web 14 is arranged to be advanced in the direction of the arrow 15 sequentially through two such sets A-1 and A2, but it will be appreciated that any number of selective particle separating sets -up to An (not shown) may be employed. Immediately following the heating coil assembly 10.1 of the first set Al, in a position to coact with the web 14 before it passes under the hopper 18 .2 of the second set A2, there is located a gaseous particle stirring arrangement 56 comprising a plenum chamber 56.1 and a series of nozzles 56.2 arranged across the web 14 as shown more clearly in FIG. 9. Another similar particle-stirring arrangement 56 follows the heating coil assembly 10.2 of the second set A2. The purpose of the particle-stirring assemblies 56 is to blow away the loose particles of electrically nonconductive material not adhering to the web 14 after passage of the web '14 through each of the heating coil assemblies 10.1, 10.2 10.n. In practice, each plenum chamber 56.1 will be connected to a source (not shown) of air or other gas under suitable pressure for this purpose. It will be appreciated that if the web 14 is taken up on a take-up roll like the 'roll 17 in FIG. 1 after passage through a number n of selective particle separating sets A-1, A2 A-n, there will be no need'for a particle-stirring arrangement 56 following the last such set in the series. In this manner a single web 14 can be used to collect electrically conductive particles captured from a series of hoppers 18 .1, 18.2 18.11 so that the web 14 will collect a greater density of electrically conductive particles than would be the case if it were .passed through only one selective particle separating set A as in .FIG. 1, all other factors being equal.

FIG. 10 illustrates an arrangement similar to FIG. 8 employing a plurality of selective particle separating sets B of FIG. 3, in series. Here the web 14 passes in the direction of the arrow 15 under a firstsuch set B-1, and

then under a first particle-stirring arrangement 56, and from there under a second separating set B-2 and a second particle-stirring arrangement 56, thence under a third separating set B-3 and a third stirring arrangement 56, as so forth under any desired number of separating sets B-n until the web 14 has collected the full amount of electrically conductive particles that it is desired to collect. It will be understood that supply and take-up rolls, like the rolls 16 and 17 in FIG. 1, and platforms like the platforms 13 (FIG. 1) and 24 (FIG. 3) may be used with the arrangements according to FIGS. 8 and 10. If desired, two or more different frequencies may be employed, in an arrangement according to FIG. 8 or FIG. 10 by arranging to drive the first selective particle separating set Al or B1 at one frequnency (e.g., 400

kc./sec.), and the next set A2 or B-2 at another fre quency (e.g., 40 mc./sec.), and so on, repeating this sequence of frequencies to the last set A-n or 13-11.

The method of my invention can be practiced with electrostatic as well as magnetic heating. Electrostatic heating is useful, for example, in separating metal salts from other particulate materials. FIGS. 11 and 12 illustra-te an electrostatic field heating unit which may be used in place of the magnetic field units 1tl.11--12 and 20-2122 which are shown in FIGS. 1 and 3, respectively. In these figures a mounting form 61 of electrically nonconductive material has electrically conductive plates 62 and 63 on two opposite inner surfaces. A platform 64 identical in structure and purpose to the platform 13 of FIG. 1 is supported within the form 61 for use in the arrangement according to FIG. 1. The form 61 is shown square in cross-sectional shape, as in FIG. 12, but may, if desired, be round or of any other suitable shape. progress of a particle collecting web (not shown) like the web 14 in FIG. 1. When this unit is used in an arrange ment according to FIG. 3, the platform 64 may be omitted, :and the particle mixture (not shown) will be dropped or (as hereinafter described) propelled through it. FIGS. 11 and 12 omit the showing of any hopper, particle feed, or take-up rolls, since as it is stated above, the electrostatic field unit '616263 can be substituted for the magnetic field units of FIG. 1 or ,3. Material comprising ing a mixture of particles some of which can be heated to a higher temperature than others by a time-varying electrostatic field, is in either case passed between the plates 62 and 63 of the electrostatic field heating unit,

thereby being differentially heated, and the hotter particles are collected in the same manner as the electrically conductive particles in FIGS. 1 and 3.

The plates 61 and 6 2 can be supplied with a suitable time-varying potential to create a time-varying electro static field by means of a Colpitts oscillator circuit as shown in FIG. 13. This circuit comprises the plates 61 and 62 as a large capacitor, an induction coil 65 and an electron tube 66', having 13+ and B- terminals 67 and 68, respectively, and a radio frequency choke 69 between the B+ terminal 67 and the anode of the electron tube 66. 'Other components of this circuit are well known and will not be described.

It will be recognized that a plurality of electrostatic field heating units according to FIGS. 11 and 12 may be employed sequentially, in the manner illustrated in FIG. .8 or FIG. 10, if desired. Further, if it is desired to employ electrostatic fields of two or more different frequencies, successive heating units may have different frequencies applied to them, as is described above with refthrough a bottom input nozzle 71 and with raw particle input namely, a mixture like the mixture 19, at the top The arrow 15.1 shows the direction of.

72 of the chamber. The particle mixture is converted by the air into a fluidized mixture 73 which then flows through a horizontal output pipe 74 and thence in the direction of the arrow 15.2 through a heating chamber 75, which is representative of any suitable selective particle heating means, such as the magnetic field unit .1tl-1112 of FIG. 1 or -2122 of FIG. 3, or the respectively. In this case, the organization of parts is like that of FIG. 3, in that the particle mixture is treated before reaching the collecting web 14.1; however, in the particular embodiment shown in FIG. 14, the particles are propelled through the heating chamber 75 by means of the fluidizing mechanism, instead of being dropped through the chamber under the force of gravity as in FIG. 3. The fluidized mixture 74 could be propelled or dropped vertically onto the web 14.1, if desired, or even propelled vertically upward to a collecting surface on the underside of the web; in either of these cases the collecting assembly 76 would be horizontally disposed (with reference to FIG. 14).

FIG. 15 shows an alternative particle propelling mechanism in the form of a sand blasting apparatus. In this figure, which is otherwise similar to FIG. 14, a chamber 80, in which a particle mixture 19 reposes, is used as a supply of the particle mixture, anld air under high pressure is fed into a blast pipe 81 connected with a vertical take-up pipe 82 which reaches into the particle mixture. Particles of the mixture 19 are carried up through the take-up pipe 82 and mixed with the air under high pressure in the nozzle 83, whence they are propelled at relatively high speed through the heating chamber 75 in a stream 19.4 toward the collecting web 14.1. It will be appreciated that a plurality of particle propelling and selective heating arrangements according to either FIG. 14

or FIG. 15 may be employed with a single collecting web 14.1, in the same manner of FIG. 10 for example, and that in such cases the particle collecting surface of the web may be so disposed (e.g., vertically) that the. nonadhering and hence uncaptured particles can fall away from the web under the force of gravity, so that stirring devices, like the stirring arrangements 56' in FIG. 10, may be omitted.

It is possible also to employ electromagnetic wave energy for the purpose of diiferentially heating particles of different properties in a particle mixture. FIGS. 16 and 17 illustrate one such embodiment of the invention, in which a waveguide 90 is supplied with ultrahigh or very high frequency energy by means of a generator 91., which may, for example, be a magnetron or a klystron or other form of oscillator circuit. As shown, the waveguide has a rectangular cross section, and is intended for operation in the fundamental or TE mode. The fundamental mode of high frequency electromagnetic wave energy in rectangular wave guides is well known. See, for example, Department of the Army Technical Manual TM 11-673, Generation and Transmission of Microwave Energy, June 1953, Section 55 (a). Preferably, the generator will be connected to one end of the Waveguide 90 and a nonreflecting termination 92 will be connected to the other end, for the purpose of preventing the setting up of a standing wave field in the waveguide. A standing wave field might have hot and cold regions, whereas a travelling wave field would avoid having such regions and is therefore preferred. Slots 93 and 94 are cut longitudinally in the narrow side walls of the waveguide 90 and a platform 95 of dielectric material is mounted transversely in the Waveguide immediately to one side of these slots. The platform 95 is similar in purpose to the platform 13 in FIG. 1. The waveguide 90, generator 91 and termination 92 forman electromagnetic field unit 91-92, which can be substituted for the magnetic field unit 10-1112 in arrangements according to FIG. 1. The web 14, hearing particles (not shown) previously deposited in an arrangement according to FIG. 1, is passed transversely through the waveguide through the slots 93 and 94 in the direction of the arrow 15.3. For metal particle separation, the web 14 is preferably disposed for maximum coupling of metal particles with the magnetic wave field.

In another embodiment of the invention employing electromagnetic wave energy a tube 96 is supported transversely in the waveguide 90, as is shown in FIGS. 18 and 19. The tube 96 is made of dielectric material and may if desired be of the same cross-sectional shape and dimensions as the output pipe 74 of the fiuidization mechanism according to FIG. 14, in which case the tube and pipe are connected together at their ends as is shown in FIG. 19, and a fluidized stream (not shown) of particles is propelled through the tube '96 toward a collecting web (not shown) in the direction of the arrow 15.4. This arrangement is of the general type represented by FIG. 3, in which the particle mixture is treated for selective heating before coming in cont-act with the collecting web. Clearly, a plurality of tubes 96 may be used spaced along the axis of the waveguide 90' as desired so that a single wave guide may be employed to treat a plurality of streams of particles simultaneously. When the tube 96 is used, the mixture 19 can be propelled through it, according to FIG. 14 or FIG. 15, or dropped through it according to FIG. 3. If desired, a plurality of electromagnetic field units may be employed, according to FIG. 8 or FIG. 10, and, further, these may be driven at different frequencies or at a single frequency as in thecases of the other embodiments of the invention described above. I An important feature of this invention is the small amount of power required to elfect separation of metallic from nonmetallic particles. This is best appreciated by consideration of the fundamental physical principles that apply. The amount of power required for separation per unit weight of metallic particles is calculated by the use of the mathematical expressions below, in accordance with actual conditions that pertain in a preferred embodiment of the invention.

First, assume the use of a paraffin wax as a heat-sensitive body 14. This wax may be utilized as .a coating on a paper base according to FIG. 6 (wax paper). The melting temperature of this material is typically 55 centigrade (Handbook of Chemistry and Physics, 29th edition). Consequently, the metallic particles need only be heated selectively to a temperature slightly above 55 C. in order to be captured by the paraffin wax. For example, in a mixture of sand and small-diameter gold particles, the gold particles need be heated only to 6 0 C. or higher in order that they will locally melt paraifin wax on contact. It is clear that the praffin wax that is melted by the heated metal particles will then cool the small metal particles almost instantly, capturing them during the resolidification of the wax. This capture will be either on or near the surface of the'wax or in the body of the wax beneath the surface after penetration by the heated metal panticles.

If the initial temperature of the metal particles is 20 C. and the terminal temperature is 75 C., the energy required to accomplish this rise in temperature is expressed by the equation where a Q is energy in gram calories;

m is the mass in grams of the metal involved;

c is specific heat (over the given temperature range); T is the final temperature; and g T is the initial temperature.

Now assume, in a practical case, that it is desired to capture 10 grams of gold per second. The specific heat of gold, 0, in the range 20 to 75 C., is 0.0316 calories per gram per C.

Q/second: l(0.03 16) (55 17.38 calories/ second Expressed in joules/ second, or watts, this is only 17.3 8 (4.18 1 =72.8 watts,

required to separate l0 grams/second of gold from a mixture of gold particles and dry sand.

The presently preferred form of energy for selectively heating metallic particles through such a temperature range without simultaneously heating the nonmetallic particles to any significant degree is a radio frequency time-varying magnetic field. This is of the type known as induction heating. However, as is explained above, this invention employs induction heating in a novel manner in -that the particles being heated need not be, and preferably are not, in contact with each other, but are individually heated. By using an induction heating generator or generators (e.g., according to FIG. and by selecting the most efiicient frequency or combination of frequencies for the particle sizes of metals that are to be heated in the induction field, the metallic particles are heated rapidly and efliciently, while the nonmetallics are substantially unaffected and remain cold (i.e., at their original temperature).

The considerations that govern the choice of frequency of the radio frequency induction heating generator are based upon considerations that include skin effect and particle size. Skin effect, or depth of penetration of a time-varying magnetic field is expressed by for a nonmagnetic material, where s is the depth of penetration (that is the depth at which the energy level has dropped to 1/ e or 0.37 approx. times the magnitude at the surface);

p is volume resistivity of the metal being heated; f is frequency of the induction field; and e is the Naperian logarithm base.

Now, the heat energy per unit time (eddy current or induced current losses) for the condition of uniform particle heating are expressed by Wc=Kf Bm where We is heat developed;

K is a constant of proportionality; f is frequency; and

Bm is maximum flux density.

Thus, if the particle is uniformly heated, the heat developed is proportional to the square of the frequency of the induction heating field. On the other hand, the depth of penetration is inversely proportional to the square root of this same frequency, and therefore, while the frequency should be as high as possible to develop heat, an upper limit is imposed on the frequency by the skin effect. Above this upper limit, the particle is no longer uniformly heated, and only the skin is heated. Below this frequency the heat developed falls off. The optimum frequency, then, is the highest frequency which produces uniform heating of particles of a given size.

It is best according to the foregoing to select a frequency, f, such that the depth of penetration, s, is substantially equal to the radius of the particle that is to be heated. In a practical case, this is an average radius of a group of particles, and it may be desirable in some cases to use two or more frequencies (as in FIG. 5). For example, in the case of gold particles which are 25 to 75 microns in diameter, the optimum frequency range is to 50 megacycles per second. For larger particles, up to 1 0 1 millimeter in diameter, frequencies in the range to 1000 kilocycles per second are desirable.

Where conventional methods of working gold ores can separate out only nuggets and large particles down to several hundred microns in size, the methods of this invention make it possible to separate and capture all sizes, including extremely small particles of sizes in the range of tens of microns, heretofore considered lost. Where water is scarce, making conventional methods inapplicable, combinations of high frequency fields of 2 or more frequencies can be used sequentially or simultaneously to separate and capture all particles, regardless of size, since the methods'of this invention do not require the use of water or any perature-sensitive body is intended to mean any body which melts, undergoes plastic flow, or otherwise becomes adhesive to particles when heated, and includes such materials as thermoplastic materials which melt locally when in contact with a hot body or particle, and some metal alloys which melt between F. and 500 F., as well as paraffin wax. The terms first materia and second material as used in the claims are intended to include particles of different sizes of the same element or compound, as well as particles of the same or different sizes of different elements or compounds.

The embodiments of the invention which have been illustrated and described herein are but a few illustrations of the invention. Other embodiments and modifications will occur to those skilled in the art. No attempt has been made to illustrate all possible embodiments of the invention, but rather only to illustrate its principles and the best manner presently known to practice it. Therefore, while certain specific embodiments have been described as illustrative of the invention, such other forms as would occur to one skilled in this art on a reading of the foregoing specification are also within the spirit and scope of the invention, and it is intended that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

What is claimed is:

1. Method of treating a mixture of particles of at least two different materials to separate particles of a first of said materials from said mixture, comprising the steps of propelling .a gas through said mixture and thereby fluidizing said mixture in a gaseous medium, propelling the fluidized mixture past a source of energy for applying to the fluidized mixture energy which selectively heats particles of said first material to a higher temperature than particles of the remainder of said mixture, thereafter propelling said fluidized mixture with said selectively heated particles toward a temperature sensitive body and selectively capturing heated particles of said first material with said temperature-sensitive body in contact therewith, the same gas being employed under pressure for fluidizing said mixture and for propelling the same successively past said source and toward said body.

2. Method of treating a mixture of particles of at least two different materials to separate particles of a first of said materials from said mixture, comprising propelling a gas through said mixture and thereby fluidizing said mixture in a gaseous medium, propelling the fluidized mixture through a field of energy which selectively heats particles of said first material in a given time to a higher temperature than particles of the remainder of said mixture, and employing said fluidizing gas for propelling said fluidized mixture containing said selectively heated particles into contact with a body which is adherent substantially only to particles at the temperature achieved by said heated particles of said first material, whereby selectively to capture said heated particles of said first material with said body. 7

3. Method of separating metallic particles from nonmetallic particles in a particle mixture, comprising the steps of propelling a gas through said mixture and thereby fluidizing said mixture in a gaseous medium, propelling the fluidized mixture through an induction heating mag- .netic field to heat the metallic particles to a given tempera :ture higher than the temperature of the nonmetallic par- .said particles as a fluidized mixture past a source of energy for selectively heating particles of said first material to a higher temperature than particles of the remainder of said mixture, and then employing the same gas to propel said fluidized mixture with said selectively heated particles toward a temperature sensitive body for selectively capturing the higher temperature particles, said gas being in continuous motion throughout said steps.

5. Method of treating a mixture of particles of at least two ditferent materials to separate particles of a first of said materials from said mixture, comprising the steps of propelling a gas in motion under pressure through said mixture to fluidize the mixture whereby substantially to separate the particles from each other, then employing the same gas to propel said particles as a fluidized mixture past a source of energy for selectively heating particles of said first material to a higher temperature than particles of the remainder of said mixture, and then employing the same gas to propel said fluidized mixture with said selectively heated particles toward a temperature sensitive body for selectively capturing the higher temperature particles, said gas being in continuous motion throughout said steps.

6. Method of treating a mixture containing metallic particles of different sizes to separate said metallic particles from said mixture, comprising the steps of employing a gas in motion under pressure to fiuidize said mixture whereby substantially to separate the particles of said mixture from each other, then employing the same gas to propel said particles as a fluidized mixture through an electromagnetic field of at least two different frequencies selected for their ability selectively to heat said metallic particles to a higher temperature than the remainder of said mixture, and then employing the same gas to propel said fluidized mixture with said selectively heated particles toward a temperature sensitive body for selectively capturing the higher temperature particles, said gas being in continuous motion throughout said steps.

References Cited in the file of this patent UNITED STATES PATENTS Brison Oct. 6, 1959 

1. METHOD OF TREATING A MIXTURE OF PARTICLES OF AT LEAST TWO DIFFERENT MATERIALS TO SEPARATE PARTICLES OF A FIRST OF SAID MATERIALS FROM SAID MIXTURE, COMPRISING THE STEPS OF PROPELLING A GAS THROUGH SAID MIXTURE AND THEREBY FLUIDIZING SAID MIXTURE IN A GASEOUS MEDIUM, PROPELLING THE FLUIDIZED MIXTURE PAST A SOURCE OF ENERGY FOR APPLYING TO THE FLUIDIZED MIXTURE ENERGY WHICH SELECTIVELY HEATS PARTICLES OF SAID FIRST MATERIAL TO A HIGHER TEMPERATURE THAN PARTICLES OF THE REMAINDER OF SAID MIXTURE, THEREAFTER PROPELLING SAID FLUIDIZING MIXTURE WITH SAID SELECTIVELY HEATED PARTICLES TOWARD A TEMPERATURE SENSITIVE BODY AND SELECTIVELY CAPTURING HEATED PARTICLES OF SAID FIRST MATERIAL WITH SAID TEMPERATURE-SENSITIVE BODY IN CONTACT THEREWITH, THE SAME GAS BEING EMPLOYED UNDER PRESSURE FOR FLUIDIZING SAID MIXTURE AND FOR PROPELLING THE SAME SUCCESSIVELY PAST SAID SOURCE AND TOWARD SAID BODY. 